This invention relates to data communications systems.
U.S. Pat. No. 5,161,153 (Westmore-1) describes a data communications system comprising a plurality of interconnected nodes, in which each node broadcasts a sequence of messages to all the nodes, including itself. The messages are grouped into frames, each frame comprising one message from each node, and the frames are delivered to all the nodes in the same sequence.
Such a communications system can be used, for example, for co-ordinating the updating of local memories in a number of processing nodes, to ensure that each memory receives update messages in the same globally unique sequence, so that a consistent chronology of updates is maintained. This updating method is described in U.S. Pat. No. 4,562,539 (Vince).
In such a system, the problem arises of how to handle errors in transmission, and in particular how to recover from these errors while maintaining the required global ordering of the frames. The object of the invention is to solve this problem.
One known method of recovery from transmission errors is a "go-back-N" automatic repeat request system as described in EP 54,118, in which, when an error is detected, the transmitter goes back and retransmits the last N data blocks.
However, this prior proposal was concerned only with a point-to-point system involving a single transmitter and a single receiver. It is not immediately apparent how this proposal could be applied to a multi-node broadcast system, as described above, in such a way as to preserve the consistency of the chronology of the messages in all the nodes.